DESCRIPTION (Applicant's Abstract): Nearly one percent of the United States population has epilepsy. By some estimates more than 20% of those patients are inadequately treated despite a growing number of anti-epileptic medications. Resective surgery is increasingly used to treat this population, despite its high costs. Outcome with regard to seizures following epilepsy surgery has rarely been systematically or prospectively assessed in large samples, and quality-of-life, cognitive, neurologic, and psychiatric status following epilepsy surgery in the long or short-term are largely unexplored. Over the past 5 years we enrolled a 400 patient cohort in the first multi-center study of epilepsy surgery. Evaluation and treatment of these patients incorporated uniformity and technological advances, as well as reliable and validated baseline and follow-up measures of psychiatric status, cognitive function, quality-of-life, seizure severity and frequency, productive activities, and family dynamic. We propose to complete two-year follow-up on the full cohort, and extend follow-up to 5 years. We seek to define the occurrence and predictors of seizure remission, as well as improvements in quality-of-life, and stability or improvement in psychiatric, cognitive and neurologic status, based on factors in the preoperative profile and postoperative observations. We also propose to define relapse and continued remission off all medications and the predictors for successful medications withdrawal, an important yet unstudied aspect of epilepsy surgery. Our primary goals are: 1. to study the probability of achieving 1, 2, and 5 year seizure remission after epilepsy surgery, and the probability of relapse after remission over a total 5 year follow-up, as well as the prognostic significance of specified preoperative and postoperative factors; 2. to determine the probability of relapse and prediction of relapse in patients who discontinue medications after 2 year remission, and prognostic factors for successful outcome; 3. to assess self reported quality-of-life and employment status yearly for 5 years after resective epilepsy surgery, and to determine the magnitude and time course of change, and the extent to which seizure response and medication changes are associated with alterations in self-perceived health and employment; 4. to identify the nature and magnitude of changes in cognitive and neurologic status after resective epilepsy surgery, the factors that predict changes, and their resilience and functional impact over 5 years of follow-up; and 5. to prospectively assess changes in behavior and psychiatric profile yearly for 5 years and examine predictive factors in long-term prognosis of depression, anxiety and other psychiatric diagnoses, as well as family dynamics. The proposed study represents a unique multi-center effort that will result in the largest systematic study of epilepsy surgery to date, and will provide definitive answers to key questions regarding the outcomes of epilepsy surgery, their measurement, and their prediction in a contemporary patient population.